[v8] py3 migration of tools/predictable_wrapper.py

Migrate predictable_wrapper to py3. Run test in v8_presubmit.

R=liviurau@chromium.org, machenbach@chromium.org

Bug: chromium:1245634
Change-Id: I941e248ffcf12ce26a55a5f5889dab06ee74e66e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3448379Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Alexander Schulze <alexschulze@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79200}

tools/predictable_wrapper.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2017 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
@@ -31,10 +31,16 @@ TIMEOUT = 120
 # Predictable mode works only when run on the host os.
 command.setup(utils.GuessOS(), None)
 
+def maybe_decode(message):
+  if not isinstance(message, str):
+    return message.decode()
+  return message
+
+
 def main(args):
   def allocation_str(stdout):
     for line in reversed((stdout or '').splitlines()):
-      if line.startswith('### Allocations = '):
+      if maybe_decode(line).startswith('### Allocations = '):
         return line
     return None
 

tools/unittests/predictable_wrapper_test.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2017 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.

tools/unittests/testdata/predictable_mocked.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2017 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.

tools/v8_presubmit.py

@@ -743,6 +743,7 @@ def PyTests(workspace):
   for script in [
       join(workspace, 'tools', 'clusterfuzz', 'foozzie', 'v8_foozzie_test.py'),
       join(workspace, 'tools', 'release', 'test_scripts.py'),
+      join(workspace, 'tools', 'unittests', 'predictable_wrapper_test.py'),
       join(workspace, 'tools', 'unittests', 'run_tests_test.py'),
       join(workspace, 'tools', 'unittests', 'run_perf_test.py'),
       join(workspace, 'tools', 'testrunner', 'testproc', 'variant_unittest.py'),